Many contemporary automobiles incorporate automatic transmissions. An automatic transmission automatically changes the gear ratio according to the speed and load of a vehicle, avoiding the need for the driver to manually shift a gear lever. Most automatic transmission systems have a defined set of gear ratios, plus a parking pawl that locks the output shaft of transmission when the vehicle is parked. Instead of a clutch, a torque converter is generally used by automatic transmission systems, to manage the connection between the transmission system and the engine of the vehicle. Besides fully automatic transmissions, several other types of transmissions are available, such as continuously variable transmissions (CVT) and semi-automatic transmissions.
Predominantly, automatic transmission systems are hydraulically operated. Basic components may include a torque converter connected to the engine of the vehicle, and a set of planetary gears that facilitate conversion between different gear ratios within an available range. The torque converter connects the engine to the transmission system of the vehicle, and acts as a substitute the mechanical clutch that is used in manual transmission systems. The planetary gear set, generally being a compound planetary gear set, includes a set of bands and clutches actuated by hydraulic servos to provide the different forward gear ratios.
Many of the automatic transmission are select-shift type transmission, where, in the drive mode, in order to perform the gear upshift and downshift operations, the driver has to activate a switch each time, when he/she intends to step-up or step-down from the current gear position to a subsequent higher or a preceding lower gear position. The switch may be in the form of a select-switch/button provided over the steering wheel or a shift-lever, or the shift-lever itself. In a case where a vehicle is equipped with 10 or more high-speed gear ratios, for example, the driver may need to activate the switch multiple times to step-up the gear ratio from a lower gear position to a comparatively higher gear position, such as from gear position 2 to 8, or vice versa. Basically, the conventional automatic transmission systems step-up or step-down the gear ratio sequentially, and the driver cannot perform direct gear shift operations by skipping intermediate gears.
While driving on a curvilinear track and heading to a turn at high speed (i.e., at a top gear position), the driver may need to sudden drop-down to a much lower gear position, and if the turn follows a straight track again, then the driver may desire to speed up quickly to a top gear. In that case, multiple activation of gear-shift switch may be undesirable, and may also cause a delay in gear shifts. Rather, a manual drive mode transmission may provide a much better driving experience than an automatic transmission mode in those cases. Further, a sequential gear ratio change from a low gear position to a relatively higher gear position in a conventional automatic transmission system involves engagement or disengagement of multiple clutches that are not associated with the initial and the desired final gear position. Frequent actuation or de-actuation of the clutches may also impact the stability of the hydraulic control system of the transmission, and may lead to undesirable clutch behavior and driveline torque disturbances.
The process of changing the gear ratio from a gear to another gear that is more than one gear step away may require multiple engagement/disengagement of clutches, causing an overall gear shift duration. A frequent engagement and disengagement of the clutch may also cause instability in the hydraulic control system, which may eventually lead to undesired clutch behavior or driveline torque disturbance.
Therefore, a need exists for a method and a system for operating a vehicular automatic transmission in manual mode, where the shifting of the gear ratio from one gear to another gear that is more than one gear step away, may be performed in a single step (i.e., by skipping the intermediate gears).